The present invention relates generally to methods and apparatus for sealing disk drives using low thermal energy bonding techniques.
A disk drive is a device used to store information in a computing environment. In a disk drive, data is generally recorded on planar, round, rotating surfaces (which are commonly referred to as disks, discs, or platters). There are several types of disk drives, including optical disk drives, floppy disk drives, and hard disk drives. Nowadays, hard disk drives tend to be most common. Strictly speaking, “drive” refers to a device distinct from its medium, such as a tape drive and its tape, or a floppy disk drive and its floppy disk. A hard disk drive (sometimes referred to as a HDD), also referred to as a hard drive, hard disk, or fixed disk drive, is a non-volatile storage device that stores digitally encoded data on rapidly rotating platters with magnetic surfaces. Early hard disk drives had removable media; however, a HDD today is typically an encased unit with fixed media.
A typical hard disk drive includes a head disk assembly (HDA) and a printed circuit board assembly (PCBA) attached to a disk drive base of the HDA. The HDA typically includes at least one magnetic disk, a spindle motor for rotating the disk, and a head stack assembly (HSA) having an actuator assembly with at least one transducer head, typically several, for reading and writing data from the disk. The PCBA includes a servo control system in the form of a disk controller for generating servo control signals. The HSA is controllably positioned in response to the generated servo control signals from the disk controller. In so doing, the attached heads are moved relative to tracks disposed upon the disk. The heads are typically distanced from the magnetic disk by a gaseous cushion—so that they are said to “fly” over the disk. Thus, it is important that the position of the heads be well-controlled for proper reading and writing from the disk.
Hard disk drives are generally sealed to prevent dust and other external sources of contamination from interfering with operation of the hard disk heads therein. Some hard disk drives are hermetically sealed. A hermetic seal is generally understood to be an airtight seal. Note that some seals (e.g., those “sealing” air within the hard disk drive) are not literally air tight, but rather utilize an extremely fine air filter in conjunction with air circulation inside the hard drive enclosure. The spinning of the disks causes air to circulate therein, forcing any particulates to become trapped on the filter. The same air currents also act as a gas bearing, which enables the heads to float on a cushion of air above the surfaces of the disks. However, “hermetically” sealed means that the seal is so airtight that the disk drive's internal pressure is substantially independent of the external or ambient pressure. This is in contrast to a conventional or non-hermetically sealed disk drive that has a breather port with a filter in a wall of the base plate or cover for equalizing the disk drive's internal pressure with the external pressure. Thus, a hermetically sealed drive does not contain a breather port.
Within a hermetically sealed hard disk drive, gases other than atmospheric air are often employed. Filling the sealed environment of a hard disk drive with gases other than air can enhance their performance. For example, use of lower density inert gases, such as helium, can reduce aerodynamic drag between the disks and their associated read/write heads by a factor of approximately five-to-one as compared to their operation in air. This reduced drag beneficially results in reduced power requirements for the spindle motor. A helium-filled drive, thus, uses substantially less power than a comparable hard disk drive operating in an air environment. At the same time, the helium gas also conducts heat generated during operation of the disk drive away more effectively than air.
Hermetically sealed hard disk drives are first filled with a desired gaseous medium (whether it be atmospheric air or one or more other gases) before operation. Then, if the constituency of the gaseous medium substantially changes due to leakage of the hard disk drive housing, the hard disk drive must be either discarded or refilled with the desired gaseous medium. Filling disk drives to a desired pressure and concentration of gaseous components, however, can be both time-consuming and difficult. A number of patent documents focus on providing and/or replenishing gases such as helium at a desired concentration within a hard disk drive. See, for example, U.S. Patent Publication Nos. 2003/0081349 and 2003/0089417. Also see U.S. Pat. No. 6,560,064.
Due to imperfect sealing of hard disk drive housings, the benefits of using lower density gases such as helium are conventionally not longstanding. Potential paths of leakage (allowing both air flow into the hard disk drive housing and allowing gas outflow from the hard disk drive housing) include those paths existing at the junction of two mating components thereof. Those components include, for example, screws or other mechanical fasteners used to conventionally fasten multiple parts of the housing together. In addition, gasket seals and the like used to improve the seal between multiple components are often susceptible to at least some leakage. As gas such as helium leaks out of a sealed hard disk drive, air leaks in (or vice versa), causing undesirable effects in the operation of the disk drives—even possibly causing the disk drives to catastrophically fail. For example, an increased concentration of air inside the hard disk drive may increase forces on the read/write head therein due to turbulent airflow within the drive. Further, such undesired air may cause the read/write heads to “fly” at too great a distance above the disks. The risk of unexpected failure due to inadequate concentration of helium within such drives is a considerable drawback to helium-filled disk drives, particularly since the data stored within the disk drive can be irretrievably lost if the disk drive fails.
Therefore, as discussed in U.S. Patent Publication No. 2003/0179489, despite the advantages of helium-filled drives, such drives have not been commercially successful. This is mainly due to problems associated with leakage of gas from within the drives over time. Unlike air-filled disk drives, helium-filled drives do not include a filtered port to equalize the pressure within the drive to the ambient pressure—which ensuing pressure differential contributes to increased leakage of gas. Thus, while prior art helium drives are completely “sealed” in the conventional sense, it is still possible for helium gas therein to leak out past conventional rubber gasket seals used to seal the top cover to the drive base. Such leakage is not surprising given the relatively smaller size (i.e., lower atomic weight) of the helium atoms in comparison to the constituent gases found in air (i.e., nitrogen and oxygen). That is, the rubber gasket seals on prior art drives allow the relatively smaller helium atoms to diffuse through the rubber membrane. Indeed, such prior art gasket seals do not provide hermetic seals with respect to air (i.e., the gasket seals are also permeable to the larger atoms of nitrogen and oxygen in air) since it is air that typically displaces the helium gas that leaks from the drive.
Most prior art gasket seals are only intended to keep relatively large contaminants such as dust or smoke from the interior of a disk drive. However, such gasket seals are preferred as compared to other, more permanent methods of sealing a drive for two main reasons. First, such seals typically do not outgas and, thus, do not contribute to the contamination of the interior of the drive. Secondly, such seals may be reused if necessary during the assembly of the disk drive, such as when an assembled drive fails to pass certification testing and must be “re-worked.” Re-working a drive typically entails removing the top cover from the base and replacing a defective disk or read/write head while the drive is still in a clean room environment. The reworked drive is then reassembled, which can even be done using the same rubber gasket seal positioned between the base and the top cover. Unfortunately, however, while such gasket seals are convenient, they simply often do not provide a sufficient hermetic seal to maintain the required concentration of helium (or other low density gas) within the disk drive for the desired service life of the drive.
In view of the potential for long-term performance problems, U.S. Patent Publication No. 2003/0179489 describes a disk drive assembly having a sealed housing. As described therein, a disc drive includes a base plate supporting a spindle motor and an actuator assembly. A structural cover is removably attached to the base plate to form an internal environment within the disc drive. The internal environment of the drive is filled with a low density gas such as helium, and a sealing cover is permanently attached to the base plate and the structural cover to form a hermetic seal that maintains a predetermined concentration of the low density gas within the internal environment over a service lifetime of the disc drive.
The disc drive further includes a first seal secured between the base plate and the structural cover to prevent contaminants from entering the internal environment of the disc drive. The first seal is formed from a material such as rubber that allows leakage of the low density gas from the internal environment at a sufficiently low rate so that the disc drive may be operated for a predetermined period of time in the absence of the sealing cover.
In one embodiment, the base plate includes a raised outer edge and the sealing cover includes a downward depending edge that is adhesively bonded within a groove formed between an outer surface of the structural cover and the raised outer edge of the base plate. Alternatively, the sealing cover may include a downward depending edge that is adhesively secured to an outer perimeter wall of the base plate. In an alternative embodiment, the sealing cover is soldered to a top surface of the raised outer edge of the base plate. Such assemblies purportedly create a hermetic seal that will maintain desired concentrations of helium (or other low density gases) within the drive over the operational lifespan of the drive (e.g., leaking helium at such a low rate that it would take over seventy years for the helium concentration to drop below a predetermined lower limit). However, such sealing covers are not without their limitations—e.g., those dimensional limitations discussed in U.S. Patent Publication No. 2003/0179489 and the potential interference of such sealing covers with electrical connectors, such as those associated with flex circuitry protruding from the disk drive. Thus, improvements are still needed.
In addition, while U.S. Patent Publication No. 2003/0223148 (corresponding to U.S. Pat. No. 7,119,984) discusses improved containment of helium within a hard disk drive, the methods therein rely on laser-based metal sealing of such drives. Further, such “sealing” of drives is incomplete in that it does not prevent leakage through valves and ports used to inject gas into disk drive housings once sealed as such. As described therein, a base can be combined with a cover by overlapping respectively corresponding coupling flanges of the base and cover with each other. The coupling flanges are then described as being jointed and fastened together by spot welding, but only if both of the base and cover are made of metal including iron. Alternatively, hermetic sealing to some extent is said to be guaranteed if seam-welding is effected by continuously carrying out spot welding. Alternatively, when the base and the cover are made of a metal other than iron or a resin material, the coupling flanges are described as being joined together by means such as wrap-seaming, screws, or riveting. Still further, if both the base and cover are made of metal including aluminum or made of a resin material, the coupling flanges are stated to be preferably jointed and fastened together by screws or rivets. Further, in the outer peripheral portion of the jointed coupling flanges, a frame composed of a pair of L-shaped frame elements can be attached to force the jointed coupling flanges to be closed up tightly. Each of these L-shaped frame elements are made of so-called engineering plastic, e.g., polyamide resin or polyphenylene sulfide resin, and have a sectional form with a recess corresponding to the outer shape of the jointed coupling flanges. In this case, the L-shaped frame elements are fixed to the jointed coupling flanges of the housing by adhesive or by welding the frame elements per se. Also see U.S. Pat. No. 6,762,909 for a description of laser welding of a disk drive's cover and base plate made of aluminum or other alloys. Similarly, U.S. Pat. No. 5,608,592 discusses how spot welding can be used to secure a base and cover of a disk drive housing.
U.S. Pat. No. 4,686,592 discloses a housing comprising a lower body portion and a cover portion. Lower body portion is stated to be cylindrical in shape, having a lip located towards the outer periphery and a ledge associated therewith. Cover portion is stated to have a lip portion along its outer periphery. The inner and outer diameter of the lips are selected so that the two lips nest with one another when the cover portion is placed over the lower body portion, i.e., the outer diameter of the lower body portion's lip is selected to be greater than the inner diameter of the cover portion's lip. Further, the height of the cover portion's lip is selected with respect to the height of the lower body portion's lip so that a groove is formed for accommodating the outer periphery of the disk. Adhesives, such as epoxy, can be applied in the groove to assist in fixedly securing the disk within the groove. The disk is further secured in the groove by the clamping action provided by the cover portion and the lower body portion. Alternative methods for securing the cover portion to the lower body portion described therein include: threading, cam-locking, radial crimping, laser welding, ultrasonic welding, and the like.
U.S. Pat. Nos. 6,392,838 and 6,525,899 disclose a disk drive assembly purportedly hermetically encased within a metallic can. The metallic can comprises a top and bottom housing. Each housing component includes a sealing flange extending around its periphery. After the disk drive assembly is securely placed into the bottom housing, the top and bottom housings are mated and sealed together by forming a seam seal with the seal flanges. Also disclosed is use of a metallic gasket seal having a C-shaped cross-sectional area to purportedly hermetically seal a disk drive assembly. The C-seal includes a base layer and a plating layer, with the length of the seal extending the periphery of the disk drive base, similar to conventional elastomer gasket seals. After the disk drive cover is placed over the disk drive base and C-seal, the cover is clamped, thus compressing the C-seal. The resulting compression forces the plating layer to fill surface asperities in the area of the disk drive cover and base that contact the C-seal. These configurations purportedly provide assemblies with atmosphere leak rates of less than one cubic centimeter per 108 seconds or 5% of the volume of the sealed atmosphere over ten years.
U.S. Pat. No. 5,454,157 describes a disk drive assembly containing a metallic base and cover. In order to minimize escape of helium or nitrogen contained therein (via porosity in the metallic base and cover plates), a special electrostatic coating process and material called “E-coat” are used. E-coating, which is said to be a commercially available coating material and is known to be an insulative epoxy material, is applied to the surfaces of the base and cover as well as all other surfaces making up the hermetically sealed chamber. Such application of the E-coating takes place before the plates are assembled together. Every surface, inner and outer, of each plate is completely coated with a black E-coating as such. With the E-coating applied, the overall sealed chamber's porosity is purportedly lowered ninety-seven percent to an acceptable amount in order to contain the helium and nitrogen gas.
Elimination of or minimization of leakage is desired for not only better containment of gas within a hard disk drive, but for other reasons as well. One such reason relates to a reduction of complications arising from electromagnetic interference. Electromagnetic interference (“EMI,” also called radio frequency interference or “RFI”) is a usually undesirable disturbance caused in an electrical circuit by electromagnetic radiation emitted from an external source. Such disturbance may interrupt, obstruct, or otherwise degrade or limit the effective performance of the circuit. EMI can be induced intentionally for radio jamming, as in some forms of electronic warfare, or unintentionally, as a result of spurious emissions and responses, intermodulation products, and the like. A source of EMI may be any object, artificial or natural, that carries rapidly changing electrical currents, such as another electrical circuit or even the sun or Northern Lights. Broadcast transmitters, two-way radio transmitters, paging transmitters, and cable television are also potential sources of EMI within residential and commercial environments. Other potential sources of EMI include a wide variety of common household devices, such as doorbell transformers, toaster ovens, electric blankets, ultrasonic pest controls (e.g., bug zappers), heating pads, and touch-controlled lamps.
It is known that EMI frequently affects the reception of AM radio in urban areas. It can also affect cell phone, FM radio, and television reception, although to a lesser extent. EMI can similarly affect performance of a computer.
In conventional disk drives, unwanted and potentially problematic EMI wavelengths can enter a disk drive through a number of places. For example, similar to paths of gas leakage, such wavelengths can enter disk drive housings around screws used to hold multiple components of the housing together.
Within integrated circuits, the most important means of reducing EMI are: the use of bypass or “decoupling” capacitors on each active device (connected across the power supply and as close to the device as possible), risetime control of high-speed signals using series resistors, and VCC filtering. If all of these measures still leave too much EMI, shielding such as using radio frequency (RF) gasket seals (which are often very expensive) and copper tape has been employed. Another method of reducing EMI is via use of metal hard disk drive components. While the use of metal components undesirably increases the overall weight of an apparatus, use of metal components has been conventionally mandated in the hard disk drive industry due to the EMI sensitivity of mechanical spinning components therein. Without mechanical spinning components therein, however, manufacturers of flash drives have taken advantage of the benefits of, for example, a plastic case for enclosure of the drive. See, for example, U.S. Pat. No. 7,301,776, which describes how metal material used for top and bottom plates of the drives described therein can be replaced by plastic as there are fewer EMI issues associated with flash memory devices as compared to mechanical spinning hard disk drives.
Another source of potential hard disk drive failure stems from electrostatic discharge (ESD). ESD refers to a sudden and momentary electric current that flows between two objects at different electrical potentials. The term is usually used in the electronics and other industries to describe momentary unwanted currents that may cause damage to electronic equipment. Ways to eliminate problematic ESD are in need of improvement as performance demands of hard disk drives increase.
While the aforementioned problems typically arise based on events and/or materials external to a disk drive, other problems may arise based on events and/or materials internal to a disk drive. For example, design of components within conventional hard disk drives can contribute to hard disk drive failure. For example, plastic components are susceptible to outgassing and components made from conductive materials are prone to shedding of particles, both of which can cause catastrophic disk failure.
Alternative methods and apparatus for joining disk drive components are, thus, desired. While welding has been used for joining disk drive housing components, as discussed above, those methods have been conventionally limited in their applications and materials, focusing predominantly on joining of metal components conventionally used for disk drive housing components.
Laser welding was first demonstrated on thermoplastics in the 1970s, but has only recently found a place in industrial-scale situations (e.g., in the mass production of syringes). The technique uses a laser beam to melt the plastic in the joint region. The laser generates an intense beam of radiation (usually in the infrared area of the electromagnetic spectrum) that is focused on the material to be joined, providing very good control over the region heated and the amount of heat applied. Two general forms of laser welding exist: direct laser welding and transmission laser welding. Direct laser welding usually uses CO2 laser radiation, which is readily absorbed by plastics, allowing quick joints to be made, but limiting the depth of penetration of the beam and restricting the technique to film applications. The shorter wavelength radiation produced by Nd:YAG, fiber and diode lasers is less readily absorbed by plastics, but these lasers are suitable for performing transmission laser welding. In this operation, it is necessary for one of the plastics to be transmissive to laser light and the other to absorb the laser energy, to ensure that the heating is concentrated at the joint region. Alternatively, an opaque surface coating may be applied at the joint to weld two transmissive plastics. Transmission laser welding is capable of welding thicker parts than direct welding, and since the heat-affected zone is confined to the joint region, no marking of the outer surfaces occurs.
In view of the number of potential problems impacting effective and long-term performance of disk drives, alternative methods and apparatus for improved sealing of disk drives are desired. Most desired are those methods and apparatus with improved efficiency and reliability over conventional attempts to provide the same.